Ablation probe with heat sink

ABSTRACT

An ablation device includes an electrode having an enclosed lumen, and a heat sink located within the lumen. An ablation device includes an elongated body, an electrode secured to the elongated body, and a heat sink connected to the electrode, wherein the heat sink is confined by the electrode and at least a portion of the elongated body. An ablation device includes an electrode, and a heat sink connected to the electrode, wherein the heat sink is not connected to a pump.

This application is a continuation of U.S. patent application Ser. No.11/090,515, filed on Mar. 25, 2005, now U.S. Pat. No. 7,670,336, thedisclosures of which is expressly incorporated herein by reference.

FIELD OF THE INVENTION

The field of the invention relates generally to ablation devices for thetreatment of tissue, and more particularly, to ablation devices havingheat dissipation capabilities.

BACKGROUND

Tissue may be destroyed, ablated, or otherwise treated using thermalenergy during various therapeutic procedures. Many forms of thermalenergy may be imparted to tissue, such as radio frequency electricalenergy, microwave electromagnetic energy, laser energy, acoustic energy,or thermal conduction. In particular, radio frequency ablation (RFA) maybe used to treat patients with tissue anomalies, such as liver anomaliesand many primary cancers, such as cancers of the stomach, bowel,pancreas, kidney and lung. RFA treatment involves destroying undesirablecells by generating heat through agitation caused by the application ofalternating electrical current (radio frequency energy) through thetissue.

Various RF ablation devices have been suggested for this purpose. Forexample, U.S. Pat. No. 5,855,576 describes an ablation apparatus thatincludes a plurality of electrodes (tines) deployable from a cannula.Each of the electrodes includes a proximal end that is coupled to agenerator, and a distal end that may project from a distal end of thecannula. The electrodes are arranged in an array with the distal endslocated generally radially and uniformly spaced apart from the distalend of the cannula. When using the above described devices inpercutaneous interventions, the cannula is generally inserted through apatient's skin, and the tines are deployed out of the distal end of thecannula to penetrate target tissue. The electrodes are then energized toablate the target tissue. The electrodes may be energized in a bipolarmode (i.e., current flows between closely spaced electrode) or amonopolar mode (i.e., current flows between one or more electrodes and alarger, remotely located common electrode) to heat and necrose tissuewithin a precisely defined volumetric region of target tissue.

Ablation devices have also been implemented using catheters. Physiciansmake use of catheters today in medical procedures to gain access intointerior regions of the body to ablate targeted tissue areas. Forexample, in electrophysiological therapy, ablation is used to treatcardiac rhythm disturbances. During these procedures, a physician steersa catheter through a main vein or artery into the interior region of theheart that is to be treated. The physician places an ablating elementcarried on the catheter near the cardiac tissue that is to be ablated.The physician directs energy from the ablating element to ablate thetissue and form a lesion. Such procedure may be used to treat atrialfibrillation, a condition in the heart in which abnormal electricalsignals are generated in the endocardial tissue.

Ablation catheters typically have an elongated shaft carrying anelectrode at its distal end. Lesions of different shapes and sizes maybe formed by choosing a suitable electrode shape or size, and/or bymanipulating the position of the electrode at the distal end of thecatheter. An ablation catheter may also have a steering mechanism forsteering its distal end, which is beneficial because it allows aphysician to steer the catheter through veins and vessel junctions. Italso allows the physician to accurately position the electrode carriedat the distal end at a target site to be ablated. Steerable ablationcatheters have been described in U.S. Pat. Nos. 6,033,378 and 6,485,455B1, the disclosures of which are expressly incorporated by referenceherein.

During use of an ablation device, the electrode delivering ablationenergy may overheat, thereby causing tissue charring and preventingformation of a deeper lesion. This may negatively affect the ablationcatheter's ability to create a desirable lesion. An overheated electrodemay also cause healthy tissue adjacent the target site to be heated.Furthermore, an overheated electrode may cause blood to be heated,thereby creating an undesirable embolism. As such, an ablation devicethat is capable of cooling an electrode is very desirable.

Ablation devices that have cooling capability are generally connected toa pump via a fluid delivery tube. The pump delivers cooling fluid to theablation device for cooling an electrode on the ablation device.However, cooling systems that require use of the pump and the fluiddelivery tube may be expensive to design and implement, and may beinconvenient and a nuisance to use. For examples, during an operation,the fluid delivery tube connecting the pump and the ablation device maytangle with another medical equipment, or may interfere with theoperation. Also, the pump may produce noise that interfere with aphysician's concentration, and may disturb conversation betweenoperators in the operation room. In addition, fluid may leak at thepump, at the fluid delivery tube, or at the ablation device. Further,for steerable ablation catheters, if not designed or constructedproperly, the fluid delivery tube inside the catheter may kink or buckleduring use. For the foregoing reasons, cooling an electrode using fluiddelivered from a pump may not be desirable.

Thus, there is currently a need for an improved ablation device that iscapable of cooling an electrode during use. Also, it would be desirablethat such ablation device does not require use of a pump.

SUMMARY

In accordance with some embodiments, an ablation device includes anelectrode having an enclosed lumen, and a heat sink located within thelumen.

In accordance with other embodiments, an ablation device includes anelongated body, an electrode secured to the elongated body, and a heatsink connected to the electrode, wherein the heat sink is confined bythe electrode and at least a portion of the elongated body.

In accordance with other embodiments, an ablation device includes anelectrode, and a heat sink connected to the electrode, wherein the heatsink is not connected to a pump.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention. It should be noted that the figures are notdrawn to scale and that elements of similar structures or functions arerepresented by like reference numerals throughout the figures. In orderto better appreciate how the above-recited and other advantages andobjects of the present inventions are obtained, a more particulardescription of the present inventions briefly described above will berendered by reference to specific embodiments thereof, which areillustrated in the accompanying drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an ablation device in accordance with some embodiments;

FIG. 2 is a partial cross sectional view of the ablation device of FIG.1 in accordance with some embodiments;

FIG. 3 is a partial cross sectional view of the ablation device of FIG.1 in accordance with other embodiments;

FIG. 4 is a partial cross sectional view of the ablation device of FIG.1 in accordance with other embodiments;

FIG. 5 is a partial cross sectional view of the ablation device of FIG.1 in accordance with other embodiments;

FIG. 6 is a partial cross sectional view of an ablation device having aheat sink employed with a ring electrode in accordance with otherembodiments;

FIG. 7 is a partial cross sectional view of an ablation device having aheat sink employed with an electrode that has a flat distal surface inaccordance with other embodiments;

FIG. 8 is a cross-sectional side view of an ablation device having heatsink(s) employed with elongated electrodes in accordance with someembodiments, showing electrodes constrained within a cannula.

FIG. 9 is a cross-sectional side view of the ablation device of FIG. 8,showing the electrodes deployed from the cannula.

FIG. 10 is a perspective view of an ablation device having heat sink(s)employed with two ring electrodes in accordance with other embodiments;and

FIG. 11 is a partial cross sectional view of the ablation device of FIG.1, showing the device having a temperature sensor.

DETAILED DESCRIPTION

FIG. 1 illustrates an ablation device 10 in accordance with someembodiments. The ablation device 10 includes an elongated body 12 havinga distal end 14 and a proximal end 16, an electrode 18 secured to thedistal end 14, and a handle 20 secured to the proximal end 16. Duringuse, the ablation device 10 is connected to a generator 24, so that RFenergy can be delivered to the electrode 18. The ablation device 10 alsoincludes a heat sink 30 located within the electrode 18. The heat sink30 is configured to carry heat away from the electrode 18 during use.

In the illustrated embodiments, the generator 24 is a radio frequency(RF) generator that delivers RF energy to ablate tissue. However, othertypes of energy, e.g., laser energy, may also be used for tissueablating purposes. In the illustrated embodiments, the ablation device10 operates in a unipolar mode. In this arrangement, the generator 24may include an indifferent patch electrode (not shown) that attaches tothe patient's back or other exterior skin area. In this case, ablationenergy will flow from the electrode 18 to the patch electrode.Alternatively, the ablation device 10 can be operated in a bipolar mode,in which case, ablation energy will flow from the electrode 18 to anadjacent electrode on the elongated body 12, or vice versa.

The elongated body 12 has a cross-sectional geometry that is circular.However, other cross-sectional shapes, such as elliptical, rectangular,triangular, and various customized shapes, may be used as well. Theelongated body 12 may be preformed of an inert, resilient plasticmaterial that retains its shape and does not soften significantly atbody temperature, like Pebax®, polyethylene, or Hytrel® (polyester).Alternatively, the elongated body 12 may be made of a variety ofmaterials, including, but not limited to, metals and polymers. Theelongated body 12 is preferably flexible so that it is capable ofwinding through a tortuous path that leads to a target site, i.e., anarea within the heart. Alternatively, the elongated body 12 may besemi-rigid, e.g., by being made of a stiff material, or by beingreinforced with a coating or a coil, to limit the amount of flexing. Thestiffness or flexibility of the elongated body 12 is a matter of designchoice, and will depend on the particular application.

The electrode 18 can be made of a solid, electrically conductingmaterial, such as, e.g., platinum or gold, that is attached to theelongated body 12. Alternatively, the electrode 18 can be formed bycoating the distal end 14 of the elongated body 12 with an electricallyconducting material, such as, e.g., platinum or gold. The coating can beapplied using sputtering, ion beam deposition, or equivalent techniques.

The handle 20 includes a steering mechanism 22 for steering the distalend 14 of the elongated body 12. The steering mechanism 22 includes arotatable cam 26 and one or more steering wires (not shown) connectedbetween the cam 26 and the electrode 18 (or the distal end 14). Duringuse, the cam 26 can be rotated to apply tension to a steering wire,thereby causing the distal end 14 of the elongated body to bend. Furtherdetails regarded the steering mechanism 22 are described in U.S. Pat.No. 5,273,535, the entire disclosure of which is herein incorporated byreference. In other embodiments, the handle 20 does not include thesteering mechanism 22.

FIG. 2 illustrates a partial cross section of the ablation device 10 inaccordance with some embodiments. As shown in FIG. 2, the electrode 18has a lumen 202 and is secured to the distal end 14 of the elongatedbody 12. A wire 201 is provided to deliver energy from the generator 24to the electrode 18 to energize the electrode 18 during use. The heatsink 30 is confined by the electrode 18 and at least a portion of theelongated body 12. Particularly, the heat sink 30 is located within thelumen 202 of the electrode 12 and a lumen 210 of the elongated body 12.In the illustrated embodiments, the elongated body 12 further includes awall 200 for confining the heat sink 30. In some embodiments, the wall200 is located at or adjacent to the distal end 14. In such cases, theheat sink 30 is confined at the distal end of the ablation device 10.Alternatively, the wall 200 can be located at another location along thelength of the body 12. For example, the wall 200 can be located at theproximal end 16, in which cases, the heat sink 30 extends from theelectrode 18 to the proximal end of the elongated body 12.

The heat sink 30 is configured to carry heat away from the electrode 18,thereby providing a cooling effect for the electrode 18 during use.Cooling causes the electrode-tissue interface to have lower temperaturevalues. As a result, the hottest isothermal region is shifted deeperinto the tissue. An electrode that is connected to a heat sink can beused to transmit more ablation energy into the tissue, compared to thesame electrode that is not connected to a heat sink.

The heat sink 30 can be made from a variety of materials. In someembodiments, the heat sink 30 can be fluid, such as water, saline, oil,or other chemical agents. The heat sink 30 is preferred to have aboiling point that is higher than 90° C., and more preferably, higherthan 100° C. However, in other embodiments, the heat sink 30 can be afluid having other boiling points. During use, as a distal portion 204of the heat sink 30 connected to the electrode 18 carries heat away fromthe electrode 18, fluid at the distal portion 204 of the heat sink 30 isheated. Due to a temperature differential between the distal portion 204and a proximal portion 206 of the heat sink 30, the heated fluid willmove towards the proximal direction, while relatively cool fluid at theproximal portion will move towards the distal direction. Once the heatedfluid has traveled away from the electrode 18, it will begin to cooldown, and will travel back towards the electrode 18 to carry additionalheat away from the electrode 18. As such, fluid of the heat sink 30 willcontinue to move within the enclosed space due to convection as the heatsink 30 is used to carry heat away from the electrode 18.

In other embodiments, instead of fluid, the heat sink 30 can be madefrom a solid material, such as ceramic. In such cases, the heat sink 30can be segmented, or can include a plurality of blocks or particles,thereby allowing the heat sink 30 to change shape when the elongatedbody 12 is bent. Alternatively, if the elongated body 12 is not intendedto be bent during use (e.g., the elongated body 12 is made from a rigidmaterial), the heat sink 30 can be manufactured as a one or morecomponents. The elongated body 12 can be made from a flexible thatallows the body 12 to expand as the heat sink 30 undergoes thermalexpansion. Alternatively, a gap can be provided between the heat sink 30and the interior wall of the elongated body 12, thereby allowing theheat sink 30 to undergo thermal expansion without radially expanding theelongated body 12.

In further embodiments, the heat sink 30 can be a gel, such as Alginate.Also, in other embodiments, the heat sink 30 can include a mixture oftwo or more of fluid (e.g., gas or liquid), solid, and gel.

In some embodiments, the ablation device 10 further includes a containerfor containing the heat sink 30. In such cases, the container is simplyinserted into the lumen 210 of the elongated body 12 during amanufacturing process. The container can be made from a rigid material,or a flexible material (e.g., to form a deformable membrane).

In alternative embodiments, instead of confining the heat sink 30 in thelumen 202 of the electrode 18, the heat sink 30 can be located within awall 220 of the electrode 18. In such cases, the heat sink 30 issubstantially confined within the wall 220 of the electrode 18 andwithin a side wall 230 of the elongated body 12, and the ablation device10 does not include the wall 200. Such configuration is beneficial inthat the lumen 210 of the elongated body 12 can be used for otherfunctions, such as to house a steering wire, an ablation wire, or otherelectrical or mechanical components.

FIG. 3 illustrates a partial cross section of the ablation device 10 inaccordance with other embodiments. As shown in FIG. 3, the lumen 202 ofthe electrode 18 is enclosed by a wall 300. As such, instead of using aportion of the elongated body 12 to confine the heat sink 30, the heatsink 30 is confined within the lumen 202 of the electrode 18. Suchconfiguration is beneficial in that it allows the heat sink 30 and theelectrode 18 to be manufactured as a single component, which can then besecured to the elongated body 12. In the illustrated embodiments, thewall 300 is secured to a proximal end 302 of the electrode 18. The wall300 can be made from the same material from which the electrode 18 ismade, but alternatively, can be made from a different material than thatof the electrode 18.

In the above embodiments, the heat sink 30 is completely confined withinthe lumen 210 of the elongated body 12 and/or the electrode 18. As such,the heat sink 30 operates in a “closed” system. Such configurationeliminates the need to use a pump and fluid delivery tubing, therebymaking it easier for a physician to use. Alternatively, the heat sink 30can be partially confined, thereby allowing the heat sink 30 to operatein an “open” system. FIG. 4 illustrates a partial cross section of thedevice 10 in accordance with other embodiments. The device 10 has asimilar configuration as that of FIG. 2, except that the wall 200 thatis used to confine the heat sink 30 has an opening 400. If the heat sink30 is made from a fluid or a gel, the opening 400 allows some of theheat sink 30 to exit during use. As shown in FIG. 4, the device 10 canfurther include a compartment 402 for containing the heat sink 30 thathas exited through the opening 400. Alternatively, the compartment 402can be a tube that is connected to the opening 400. Also, in alternativeembodiments, the wall 200 does not include the opening 400. Instead, thewall 230 of the elongated body 12 has an opening (not shown) forallowing some of the heat sink 30 to exit. In such cases, the wall 230further includes a channel or a lumen for housing or carrying the exitedheat sink 30.

FIG. 5 illustrates a partial cross section of the device 10 inaccordance with other embodiments. The device 10 has a similarconfiguration as that of FIG. 3, except that the wall 300 that is usedto confine the heat sink 30 has an opening 410. If the heat sink 30 ismade from a fluid or a gel, the opening 410 allows some of the heat sink30 to exit during use. As shown in FIG. 5, the device 10 can furtherinclude a compartment 412 for containing the heat sink 30 that hasexited through the opening 410. Alternatively, the compartment 412 canbe a tube that is connected to the opening 410. Also, in alternativeembodiments, the wall 300 does not include the opening 410. Instead, thewall 220 of the electrode 18 has an opening (not shown) for allowingsome of the heat sink 30 to exit. In such cases, the wall 220 furtherincludes a channel or a lumen for housing or carrying the exited heatsink 30.

In the above embodiments, the electrode 18 is a tip electrode that issecured to the distal end 14 of the elongated body 12. Alternative, theelectrode 18 can be secured to the elongated body 12 at a differentposition. For example, in other embodiments, the electrode 18 can have aring configuration, and is secured to the elongated body 12 at a pointalong the length of the elongated body 12 (FIG. 6). As shown in FIG. 6,the heat sink 30 is located within an opening 500 of the ring electrode18.

Also, instead of having the shapes illustrated previously, the electrode18 can have other shapes. For example, the electrode 18 can have a flatsurface 550 at a distal tip of the electrode 18 (FIG. 7).

In other embodiments, the ablation device 10 can include two electrodes562, 564 that are positioned relative to each other in a substantiallyconcentric configuration (FIG. 8). In such cases, the heat sink 30 canbe located within an opening 566 of the inner electrode 562 and/or thespace 568 between the electrodes 562, 564. Double ring electrodes, suchas La Placian electrodes, have been described in U.S. patent applicationSer. No. 10/318,655, filed on Dec. 12, 2002.

In other embodiments, the electrode 18 can be a needle electrode thathas an elongated shape. FIGS. 9 and 10 illustrate an ablation device 650having elongated electrodes in accordance with other embodiments. Theablation device 650 includes a cannula 652 having a lumen 654, a shaft656 having a proximal end 658 and a distal end 660, and a plurality ofelectrode 662 secured to the distal end 660 of the shaft 656. Theproximal end 658 of the shaft 656 may include a connector 663 forcoupling to a generator 612.

The cannula 652 coaxially surrounds the shaft 656 such that the shaft656 may be advanced axially from or retracted axially into the lumen 654of the cannula 652. Optionally, a handle 664 may be provided on theproximal end 658 of the shaft 656 to facilitate manipulating the shaft656. The electrodes 662 may be compressed into a low profile whendisposed within the lumen 654 of the cannula 652, as shown in FIG. 9. Asshown in FIG. 10, the proximal end 658 of the shaft 656 or the handle664 (if one is provided) may be advanced to deploy the electrodes 662from the lumen 654 of the cannula 652. When the electrodes 662 areunconfined outside the lumen 654 of the cannula 652, they may assume arelaxed expanded configuration. FIG. 10 shows an exemplary two-electrodearray including electrode 662 biased towards a generally “U” shape andsubstantially uniformly separated from one another about a longitudinalaxis of the shaft 656. Alternatively, each electrodes 662 may haveanother shape, such as a “J” shape, a flared profile, or a rectilinearshape, and/or the array may have one electrode 662 or more than twoelectrodes 662. The array may also have non-uniform spacing to producean asymmetrical lesion. The electrode 662 are preferably formed fromspring wire, superelastic material, or other material, such as Nitinol,that may retain a shape memory. During use of the ablation device 600,the electrodes 662 may be deployed into a target tissue region todeliver energy to the tissue to create a lesion. Exemplary ablationdevices having a spreading array of electrodes have been described inU.S. Pat. No. 5,855,576, the disclosure of which is expresslyincorporated by reference herein.

As shown in FIG. 10, the heat sink 30 can be located within a lumen 700of the electrode 662. In some embodiments, the heat sink 30 locatedalong portion(s) of the electrode 662. Alternatively, the heat sink 30extends substantially along the length of the electrode 662. In furtherembodiments, the heat sink 30 can extends to a lumen (not shown) that islocated within the shaft 656.

In the above embodiments, the heat sink 30 substantially occupies thespace in which it is confined. Alternatively, the heat sink 30 does notsubstantially occupy the space in which it is confined. For examples,for the case of solid, the heat sink 30 can be sized to occupy only aportion of the lumen 210 within the elongated body 12. In other cases,the heat sink 30 can be coated onto an interior surface of the electrode18, thereby leaving a substantial portion of the lumen 202 unoccupied bythe heat sink 30. Also, in other embodiments, the ablation device 10 canfurther include an inner tubular member located within the lumen 210 ofthe elongated body 12. In such cases, the heat sink 30 is located at thespace between the inner tubular member and the elongated body 12, anddoes not occupy the space within the inner tubular member.

In any of the embodiments described herein, the ablation device canfurther include a temperature sensor 800 secured to the electrode 18(FIG. 11). A signal wire 802 can be used to transmit a signal(associated with a temperature of the electrode) to a processor (notshown), which is configured to control an operation of the generator 24to thereby adjust an amount of energy transmitted to the electrode.

Although the above embodiments have been described with reference toablation devices, in other embodiments, the heat sink 30 can be employedwith other types of medical devices, which may or may not include anelectrode.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

1. An ablation device comprising: an elongated body having a proximalend and a distal end and a lumen extending at least partially from theproximal end to the distal end; an electrode disposed at the distal endof the elongated body, the electrode having a lumen in communicationwith the lumen of the elongated body; a wall disposed in one of thelumen of the elongated body and the lumen of the electrode, the wallincluding an opening therein; a tube coupled to the opening in the wall;and a liquid heat sink confined by the wall and an inner surface of theelectrode wherein the opening in the wall allows liquid heat sink toflow there through and into the tube, the liquid heat sink having aboiling point such that upon energizing the electrode the heat sinkmaintains its liquid state.
 2. The ablation device of claim 1, whereinthe boiling point of the liquid heat sink is greater than 90° C.
 3. Theablation device of claim 1, wherein the boiling point of the liquid heatsink is greater than 100° C.
 4. The ablation device of claim 1, whereinthe liquid heat sink comprises a mixture of two or more fluids.